Wildfires that raged in Victoria, Australia, for two months several years ago were associated with a 7 percent increase in sudden cardiac arrests -- an electrical malfunction that causes the heart to stop beating. Hospitalizations for heart disease rose nearly 2 percent and emergency room visits for heart disease increased more than 2 percent, researchers reported.

Men and people 65 and older were most at risk for cardiac arrests, the study found.

"Where there's fire, there's smoke, and the pollutants in the smoke can potentially have an impact on health," said lead researcher Anjali Haikerwal, from Monash University in Melbourne, Australia. The report was published July 15 online in the Journal of the American Heart Association.

For the study, researchers used data from the Victoria health registry during the wildfire period, from December 2006 to January 2007. Towns and cities are widely separated in Victoria, a state in southeast Australia of more than 87,800 square miles.

During those two months, smoke reached cities far from the fires. On most days, levels of fine-particulate air pollutants were higher than recommended limits, the researchers found.

While the researchers only found an association between pollution levels and heart hazards, they said the tiny particles of air pollution from the fires are the likely culprit. "These fine particles are easily inhaled and go deep into the lungs and then trigger various heart problems that could cause heart attacks or cardiac arrest," Haikerwal said.

These hazardous particles are less than 2.5 thousandths of a millimeter in diameter, much smaller than a speck of dust or a fraction of the width of a human hair, the researchers said. Typically, they're invisible.

The usual sources for this pollution are burning wood, burning coal and car exhaust, among others, the researchers said.

Breathing wildfire smoke is already linked to asthma, but exactly how the fine particles in smoke harm the heart isn't clear. "We need more research to understand the reasons behind this and back our study up," Haikerwal said.

Constant exposure to air pollution has been tied to heart problems before. But pollution from wildfires is unique in that it is very intense but only for a short time, Haikerwal said.

"The exposure patterns are different, and we need more research to determine which is more harmful," she said.

With wildfires burning in the western region of the United States, avoiding the polluted air is imperative for heart patients, experts said.

Stay indoors and be aware of your health, keep taking your medication and get help if you develop difficulty breathing or chest pain, Haikerwal said.

Dr. Gregg Fonarow, a spokesman for the American Heart Association, said a variety of studies "have suggested that fine-particulate matter found in air pollution can increase the risk of acute coronary events."

Everyone, especially those at risk for heart problems, should avoid exposure to this type of air pollution as much as possible, said Fonarow, a professor of cardiology at the University of California, Los Angeles, who was not involved with the study.

"These findings also support a recent American Heart Association scientific statement that characterizes this fine-particulate air pollution as a modifiable risk factor that contributes to heart disease, sickness and death," he said.